Project Summary In the wake of COVID-19 pandemic, fever with severe systemic inflammation and shock, known as Pediatric Inflammatory Multisystem Syndrome (PIMS), has evolved as a new threat to children. PIMS was originally reported in Western Europe and the number of cases is rapidly increasing in the U.S. A hallmark of PIMS has been heart failure leading to shock and the absence of significant pulmonary disease. The clinical presentation in these patients shares many features with Kawasaki disease (KD), the most common cause of acquired heart disease in children, which itself can present with distributive shock requiring inotropic and vasoactive support in the intensive care unit. Several PIMS patients are either SARS-CoV-2 PCR positive or have developed antibodies against SARS-CoV-2, suggesting that PIMS is an immune-mediated reaction to antecedent exposure to the virus. Curiously, at the same time that patients are being diagnosed with PIMS, the numbers of children with typical KD has increased dramatically in these same regions. The emergence of PIMS is so new and so rapidly evolving that there are literally no publications, treatment guidelines or clinical trials related to these seriously affected pediatric patients. Through our network of 30 pediatric centers participating in KIDCARE, our comparative effectiveness trial for treatment-resistant KD funded by PCORI, we are collecting patient data and clinical samples to support the work proposed here. The goal of this administrative supplement is to analyze demographic, clinical and laboratory data in conjunction with assays using patient cells and sera, which will allow us to study the relationships among SARS-CoV-2 infection, typical KD, and PIMS and to model different therapeutic strategies against PIMS. Three specific aims are proposed to achieve this goal. Specific Aim 1 will profile and compare clinical features of PIMS and typical KD. Demographic and clinical data and the neutrophil response to intravenous immunoglobulin (IVIG) will be compared between these two illnesses. Cytokine profiles and inflammatory markers in plasma from acute and subacute PIMS and typical KD will also be compared. Specific Aim 2 will elucidate molecular features of PIMS and compare with typical KD. We will use RNA-seq, ELISA, and Western blot analyses to profile changes in levels of molecules related to inflammation (e.g., TIFA, NFk?, NLRP3-inflammasome, IL-1, IL-6, TNF?) and cardiovascular health (KLF4, miR-483, ACE2) in endothelial cells and cardiomyocytes. Specific Aim 3 will test the efficacy of drug therapy for PIMS by comparing the in vitro effects of intravenous immunoglobulin, steroids, and anakinra on inflammatory pathways and cardiovascular biomarkers in endothelial cells and cardiomyocytes treated with sera from acute PIMS patients prior to therapy. The synergistic expertise of the investigative teams in this multi-PI supplement provides a unique opportunity to understand the clinical features, molecular basis, and efficacy of drug treatment of PIMS as compared to KD.